ARINC Protocol Tutorial Table of Contents

GE Intelligent Platforms

Chapter 1 ARINC 429 Tutorial 4 Introduction 4 About ARINC 4 What is ARINC 429? 4 ARINC 429 Usage 4 ARINC 429 Electrical Characteristics 5 Protocol 6 Bit Timing and Slew Rate 6 ARINC 429 Word Format 7 Parity 7 SSM 7 Data 7 SDI 7 Label 7 Transmission Order 7 ARINC 429 Data Types 7 BCD Data Encoding 7 BNR Data Encoding 8 Mixed Formats 9 Discrete Data Formats 9 Data Translation Method 10 Bit Oriented Protocols 11 ARINC 419 13 ARINC 453 13 ARINC 561/568 13

Chapter 2 Other ARINC Protocols 13 ARINC 575 14 ARINC 615 14 ARINC 629 14 ARINC 708 14 ARINC 717 14

Appendix A References 15 List of References 15

2 Table of Figures & List of Tables

Table of Figures Figure 1. ARINC 429 Bit Encoding Example 6 Figure 2. Slew Rates and Bit Timing Diagram 6 Figure 3. Generalized ARINC Word Format 7 Figure 4. Generalized BCD Word Format 8 Figure 5. BCD Word Format Example 8 Figure 6. Generalized BNR Word Format 8 Figure 7. Example BNR Encoding 8 Figure 8. File Transfer Scheme Version 1 (no Windows) 11 Figure 9. ARINC 561 6-Wire Bit Encoding 13 Figure 10. Harvard Bi-phase Bit Encoding 13

List of Tables Table 1. Partial List of Equipment IDs 5 Table 2. ARINC 429 Characteristic Summary 6 Table 3. ARINC Bit Characteristics 6 Table 4. SSM Codes for BCD data 7 Table 5. SSM Codes for BNR data 7 Table 6. Dedicated Discrete Example 9 Table 7. Examples of BCD Labels 9 Table 8. Examples of BNR Labels 9 Table 9. Equipment IDs for Tables 6 and 7 10 Table 10. Message Sequence for Label 241 10 Table 11. Systems Using Bit Oriented Communications and Their Address Labels 12

3 Chapter 1 ARINC 429 Tutorial

Introduction About ARINC Aeronautical Radio, Incorporated (ARINC) is a major company This document provides an overview of ARINC 429 and other that develops and operates systems and services to ensure ARINC protocols. ARINC 429 is the most commonly used data the efficiency, operation, and performance of the aviation bus for commercial and transport aircraft. This document and travel industries. It was organized in 1929 by four major explains the origins of the ARINC Corporation, the data bus airlines to provide a single licensee and coordinator of radio specification and where ARINC 429 is used. Then it summa- communications outside the government. Only airlines and rizes the principal electrical and data characteristics, which aviation-related companies can be shareholders, although are defined in the specification. all airlines and aircraft can use ARINC’s services. It is now a $280 million company with headquarters in Annapolis, This document is not a complete description of ARINC 429. It Maryland and over 50 operating locations worldwide. is intended only as a brief tutorial and isn’t meant to replace The company has two major thrusts: the complete specification, which can be purchased from • Communications and information processing services for ARINC (see Appendix A, “References” for contact information). the aviation and travel industry. • System engineering, development and integration for ARINC 429 employs unidirectional transmission of 32-bit government and industry. words over two wire twisted pairs using bipolar RZ format. This tutorial includes charts illustrating slew times and bit ARINC has provided leadership in developing specifications timing. It describes the five fields in each word and explains and standards for avionics equipment and one of these the use of labels. Messages are repeated at specified inter- specifications is the focus of this tutorial. Industry-wide vals with typical applications sending groups or frames of committees prepare the specifications and standards. ARINC messages. Examples are given of the commonly used word Specification 429 was developed and is maintained by the formats such as BNR, BCD, Discrete data, and other formats. Airlines Electronic Engineering Committee (AEEC) comprising Also explained is a newer bit-oriented protocol, sometimes members that represent airlines, government, and ARINC. called the Williamsburg Protocol, which has been introduced The General Aviation Manufacturers Association (GAMA) in to provide an improved method of transmitting files of data. Washington, D.C. also maintains a specification document Additionally, the document includes a brief explanation of with ARINC 429 labels: “ARINC 429 General Aviation Subset”. other ARINC specifications, such as 419, 561, 573, 582, 615, and 717. What is ARINC 429? ARINC 429 is a specification which defines how avionics Frequent references are made to ARINC Specification equipment and systems should communicate with each 429 and many examples are taken from it. This tutorial is other. They are interconnected by wires in twisted pairs. intended to introduce you to the subject. Individuals needing The specification defines the electrical and data character- more detail should obtain a copy of the specification from istics and protocols which are used. ARINC 429 employs a ARINC and also should consider consulting other sources unidirectional data bus standard known as Mark 33 Digital identified in the list of references. Information Transfer System (DITS). Messages are transmitted at a bit rate of either 12.5 or 100 kilobits per second This document has been prepared by GE Intelligent Platforms to other system elements, which are monitoring the bus for use by its employees and customers. GE is a full-service messages. Transmission and reception is on separate ports manufacturer of Test, Simulation, and Interface products so that many wires may be needed on aircraft, which use a for avionics data buses. The hardware and software can be large number of avionics systems. used to monitor or simulate data bus messages for analyses and for simulating bus operation. To learn about the full line ARINC 429 Usage of GE products, visit our Web site or contact us by phone or fax. Information can also be obtained via e-mail. See the ARINC 429 has been installed on most commercial transport last page of this manual for the latest contact information. aircraft including: Airbus A310/A320 and A330/A340; Bell Detailed installation and user manuals are provided with Helicopters; Boeing 727, 737, 747, 757, and 767; and McDon- each product, and demonstration software is available free nell Douglas MD-11. Boeing is installing a newer system of charge. specified as ARINC 629 on the 777 and some aircraft are using alternate systems in an attempt to reduce the weight of wire needed and to exchange data at a higher rate than

4 is possible with ARINC 429. The unidirectional ARINC 429 The specification also identifies a number of systems which system provides high reliability at the cost of wire weight are capable of interchanging files of data in a bit-oriented and limited data rates. Military aircraft generally use a format. Such files may require the transmission of a high-speed, bi-directional protocol specified in Military Speci- number of messages in sequence. Systems capable of bit- fications MIL-STD-1553. oriented communications and their addresses are listed in Table 10. The SAL is used to identify the recipient of a Each aircraft may be equipped with different electronic bit-oriented message. equipment and systems needing interconnection. A large amount of equipment may be involved depending on the ARINC 429 Electrical Characteristics aircraft. These are identified in the specification and are An ARINC 429 data bus uses two signal wires to transmit assigned digital identification numbers called Equipment 32-bit words. Transmission of sequential words is separated ID. A partial list of equipment identified in ARINC Specifica- by at least 4 bit times of NULL (zero voltage). This eliminates tion 429-15 can be found in Table 1 along with their digital the need for a separate clock signal wire. That’s why this addresses. signal is known as a self-clocking signal.

Table 1. Partial List of Equipment IDs

Eq. ID Equipment Type Eq. ID Equipment Type 001 Flight Control Computer (701) 029 ADDCS (729) and EICAS 002 Flight Management Computer (702) 02A Thrust Management Computer 003 Thrust Control Computer (703) 02B Perf. Nav. Computer System (Boeing 737) 004 Inertial Reference System (704) 02C Digital Fuel Gauging System (A310) 005 Attitude and Heading Ref. System (705) 02D EPR Indicator (Boeing 757 006 Air Data system (706) 02E Land Rollout CU/Landing C & LU 007 Radio Altimeter (707) 02F Full Authority EEC-A 008 Airborne Weather Radar (708) 030 Airborne Separation Assurance System 009 Airborne DME (709) 031 Chronometer (731) 00A FAC (A310) 032 Passenger Entertain. Tape Reproducer (732) 00B Global Positioning System 033 Propulsion Multiplexer (PMUX) (733 00D AIDS Data Management System 034 Fault Isolation and Detection System (734) 010 Airborne ILS Receiver (710) 035 TCAS (735) 011 Airborne VOR Receiver (711) 036 Radio Management System (736) 012 Airborne ADF System (712) 037 Weight and Balance System (737 016 Airborne VHF COM Receiver (716) 038 ADIRS (738) 017 DEFDARS-AIDS (717) 039 MCDU (739) 018 ATC Transponder (718) 03A Propulsion Discrete Interface Unit 019 Airborne HF/SSB System (719) 03B Autopilot Buffer Unit 01A Electronic Supervisory Control 03C Tire Pressure Monitoring System 01B Digital Flap/Slat Computer (A310) 03D Airborne Vibration Monitor (737/757/767) 01C Engine Parameter Digitizer (Engine) 03E Center of Gravity Control Computer 01D A/P & F/D Mode Control Panel -757/767 03F Full Authority EEC-B 01E Performance Data Computer (Boeing) 040 Cockpit Printer 01F Fuel Quantity Totalizer 041 Satellite Data Unit 020 DFS System (720) 046 CTU 023 Ground Proximity Warning Sys (723) 047 Digital Flight Data Recorder 024 ACARS (724) ---- additional items 025 Electronic Flt. Instruments (725) ---- “ 026 Flight Warning Computer (726) ---- “ 027 Microwave Landing System (727) 241 High Power Amplifier

5 Chapter 1 ARINC 429 Tutorial

The nominal transmission voltage is 10 ±1 volts between Table 2. ARINC 429 Characteristic Summary wires (differential) with either a positive or negative polar- ity. Therefore, each signal leg ranges between +5V and -5V. Electrical Characteristic Value If one leg is +5V, the other is 5V and vice versa. One wire is Voltage Levels, each leg with called the “A” (or “+” or “HI”) side and the other is the “B” respect to ground +5V, 0V, -5V (or “-” or “LO”) side. This is known as bipolar return-to-zero Voltage Levels, Leg A with (BPRZ) modulation. The composite signal state may be one respect to Leg B +10V, 0V, -10V Bit Encoding Bipolar Return to Zero of three levels: Word size 32 bits • HI which should measure between 7.25 and 11 volts Bit Rates 100K or 12.5K bits/s between the two wires (A to B). High Speed Slew Rate 1.5 +/- 0.5 μsec • NULL which should be between 0.5 and -0.5 (A to B). Low Speed Slew Rate 10 +/- 5 μsec • LO which should be between -7.25 and -11 volts (A to B). In most cases, an ARINC message consists of a single data The received voltage depends on line length and the number word. The label field of the word defines the type of data that of receivers connected to the bus. No more than 20 receiv- is contained in the rest of the word. ers should be connected to a single bus. Since each bus is unidirectional, a system needs to have its own transmit bus if Bit Timing and Slew Rate it is required to respond or to send messages. The slew rate refers to the rise and fall time of the ARINC The transmitting and receiving circuits must be designed for waveform. Specifically, it refers to the amount of time it takes reliably sending and detecting the null transition between the ARINC signal to rise from the 10% to the 90% voltage high and low states. The parameters vary with the type of amplitude points on the leading and trailing edges of the operation as defined in Reference 2. The slew rates and pulse. See Figure 2. tolerances are shown in Figure 1 for both 100K and 12.5K data rates. Table 3. ARINC Bit Characteristics

Protocol Parameter High Speed Low Speed ARINC 429 is a very simple, point-to-point protocol. There Bit Rate 100K bits/second 12.5K-14.5K bits/second can be only one transmitter on a wire pair. The transmitter Time Y (one bit) 10 μsec ± 2.5% 1÷(bit rate) μsec ± 2.5% is always transmitting either 32-bit data words or the NULL Time X 5 μsec ± 5% Y/2 μsec ± 5% state. There is at least one receiver on a wire pair; there may Pulse Rise Time 1.5 ± 0.5 μsec 10 ± 5 μsec be up to 20. Pulse Fall Time 1.5 ± 0.5 μsec 10 ± 5 μsec

1 2 3 4 5 6 7 8 9 10 32 Bit Number

HI +5 ••• A Null 0 ••• “A” Leg Low -5 •••

HI +5 ••• B Null 0 ••• “B” Leg Low -5 ••• 1 0 1 1 0 1 0 1 0 0 1 Data

Table 2 summarizes ARINC 429 characteristics.

Figure 1 ARINC 429 Bit Encoding Example Figure 2 Slew Rates and Bit Timing Diagram

6 ARINC 429 Word Format Data ARINC data words are always 32 bits and typically use the Bits 29 through 11 contain the data, which may be in a format shown in Figure 3 which includes five primary fields, number of different formats. Some examples are provided namely Parity, SSM, Data, SDI, and Label. ARINC convention later in the tutorial. There are also many non-standard for- numbers the bits from 1 (LSB) to 32 (MSB). mats that have been implemented by various manufacturers. In some cases, the data field overlaps down into the SDI bits. In this case, the SDI field is not used. 32 31 30 29 11 10 98 1 P SSM DATA PAD DISCRETES SDI LABEL SDI MSB LSB Bits 10 and 9 provide a Source/Destination Identifier or SDI. This is used for multiple receivers to identify the receiver for Figure 3 Generalized ARINC Word Format which the data is destined. It can also be used in the case of multiple systems to identify the source of the transmission. In Parity some cases, these bits are used for data. ARINC 429 can have The MSB is always the parity bit for ARINC 429. Parity is nor- only one transmitter on a pair of wires, but up to 20 receivers. mally set to odd except for certain tests. Odd parity means that there must be an odd number of “1” bits in the 32-bit Label word that is insured by either setting or clearing the parity Bits 8 through 1 contain a label identifying the data type and bit. For example if bits 1-31 contain an even number of “1” the parameters associated with it. The label is an important bits, bit 32 must be set to create ODD parity. On the other part of the message and is described in more detail below. hand, if bits 1-31 contain an odd number of “1” bits, the parity t is used to determine the data type of the remainder of the bit must be clear. word and, therefore, the method of data translation to use. The various data types are described in detail below. Labels SSM are typically represented as octal numbers. Bits 31 and 30 contain the Sign/Status Matrix or SSM. This field contains hardware equipment condition, operational Transmission Order mode, or validity of data content. Applicable codes are The least significant bit of each byte except the label is trans- shown in Table 4 and Table 5. mitted first, and the label is transmitted ahead of the data in each case. The order of the bits transmitted on the ARINC bus Table 4. SSM Codes for BCD data is as follows: 8, 7, 6, 5, 4, 3, 2, 1, 9, 10, 11, 12, 13 … 32. Bit Meaning Note: 31 30 When a 32-bit ARINC word is transmitted on the bus, in the case of the label, 0 0 Plus, North, East, Right, To, Above the most significant bit is transmitted first. This reverse order is in contrast to 0 1 No Computed Data the transmission order of the other bits in the ARINC word. 1 0 Functional Test 1 1 Minus, South, West, Left, From, Below ARINC 429 Data Types All ARINC data is transmitted in 32 bit words. The data type Table 5. SSM Codes for BNR data may be Binary Coded Decimal (BCD), two’s complement binary notation (BNR), Discrete Data, Maintenance Data and Bit Meaning Acknowledgment, and ISO Alphabet #5 character data. In 31 30 the newest versions, bit oriented packets of messages can be 0 0 Failure Warning used to transmit files. 0 1 No Computed Data 1 0 Functional Test BCD Data Encoding 1 1 Normal Operation BCD, or binary-coded-decimal, is a common data format found in ARINC 429 and many other engineering applications. In this format, four bits are allocated to each decimal digit. A generalized BCD message is shown in Figure 4. Its data fields contain up to five sub-fields. The most significant sub-field contains only the bits, so that its maximum decimal

7 Chapter 1 ARINC 429 Tutorial value can be 7. If the maximum decimal value is greater than positive values. If bit 29 is a ‘1’ then the number is negative (or 7, bits 29 through 27 are padded with zeros and the second South, West, Left, From, or Below). Otherwise, it is positive (or sub-field becomes the most significant. The example mes- North, East, Right, To, or Above). sage in Figure 5 conveys the data that the DME distance is 25786 and has a positive sign. The specific equipment, Figure 7 shows an example of BNR encoding. The particu- numeric scale, and location of the decimal point are a func- lar message uses label 103, which is Selected Airspeed. By tion of the label and are discussed later. referencing the ARINC 429 specification, we know that the scale is 512, and 11 bits are used (29 through 19). A zero in BNR Data Encoding bit 29 shows that this is a positive value. The numeric value BNR or “binary” encoding is also a very common ARINC data is obtained by multiplying the scale factor, determined from format. This type of encoding simply stores the data as a data type associated with the label, by the ratio indicated by binary number, much in the same format that is used on virtu- each successive bit and adding them together. Bit 28 is ½ ally every modern-day computer. Figure 6 shows the general of the scale factor (256 in this case), bit 27 is ¼ of the scale BNR format. Bit 29 is the sign bit and bit 28 is the most sig- factor, bit 26 is 1/8 of the scale factor, bit 23 is 1/64, bit 22 nificant bit of the data field, which represents one half of the is 1/128, etc. Thus, in this example, Selected Airspeed = 268 maximum value of the parameter being defined. Successive Knots (256 + 8 + 4). bits represent the increments of a binary fraction series. Negative numbers are encoded as the two’s complement of This may appear to be more complex than it really is. The

32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 1

P SSM CHAR 1 CHAR 1 CHAR 1 CHAR 1 CHAR 1 SDI LABEL

Figure 4 Generalized BCD Word Format

32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 1

P SSM 0 1 0 0 1 0 1 0 1 1 1 1 0 0 0 0 1 1 0 SDI LABEL

0 0 265 7 8

Figure 5 BCD Word Format Example

32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 1

P SSM Data Pad SDI LABEL

Figure 6 Generalized BNR Word Format

32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 1

P SSM Data Pad SDI LABEL

0 1 1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 103

Figure 7 Example BNR Encoding

8 underlying principle is conventional binary mathematics as Table 6. Dedicated Discrete Example performed by any modern day computer. A computer pro- grammer can shift the BNR data and sign bits into a program Bit Function 1 0 variable and manipulate them directly with any standard 1 Label 005 X mathematical manipulation. 2 Label 005 X 3 Label 005 X 4 Label 005 X Mixed Formats 5 Label 005 X The 32-bit message words can also include discrete infor- 6 Label 005 X mation, either mixed with BCD or BNR data, or as separate 7 Label 005 X messages. Unused bits in a word may be assigned one bit 8 Label 005 X per variable starting in Bit #11 until the data field is reached. 9 SDI 10 SDI If there are no discretes encoded the word, the unused posi- 11 PAD X tions are filled with zeros. 12 PAD X 13 Failure to clear serial data interrupt Fail Pass Discrete Data Formats 14 ARINC received fail Fail Pass A large number of ARINC 429 words are dedicated entirely to 15 PROM checksum fail Fail Pass discretes; these are spelled out in Reference 3. Table 6 shows 16 User RAM fail Fail Pass 17 NV RAM address fail Fail Pass a word used to transmit engine data. 18 NV RAM bit fail Fail Pass 19 RTC fail Fail Pass Maintenance Data 20 Microprocessor fail Fail Pass ARINC 429 also provides for transmission and acknowledg- 21 Battery low Fail Pass ment of maintenance data and alphanumeric messages. 22 NV RAM corrupt Fail Pass These functions usually involve exchanging a sequence of 23 Not used 24 Not used messages. Alphanumeric messages use ISO Alphabet No. 5. 26 Interrogate activated These message types are being superseded by a bit-oriented 27 Erase activated Activated Non-Act. protocol, which is described later in the tutorial. If you need 28 Bit activated Activated Non-Act. more information, refer to the specification. 29 SSM Activated Non-Act. Data Translation Method 30 SSM 31 SSM 32 Parity (Odd)

Table 7. Examples of BCD Labels

Label Equip ID (hex) Parameter Name Units Range Scale Digits + Res. Min. Tx Rate (ms) Max. Tx Rate (ms) 010 002 Present Position - Degrees- Latitude Minutes 180N -180S 6 N 0.1 250 500 004 Present Position - Degrees Latitude Minutes 180N -180S 6 N 0.1 250 500 038 Present Position - Degrees Latitude Minutes 180N -180S 6 N 0.1 250 500 014 004 Magnetic Heading Degrees 0 -359.9 4 0.1 250 500 005 Magnetic Heading Degrees 0 -359.9 4 0.1 250 500 038 Magnetic Heading Degrees 0 -359.9 4 0.1 250 500

Table 8. Examples of BNR Labels

Label Equip ID (hex) Parameter Name Units Range (Scale) Bits Res. Min. Tx Rate (ms) Max. Tx Rate (ms) 064 03C Tire Pressure (nose) psia 1024 10 1.0 50 250 102 002 Selected Altitude feet 65536 16 1.0 100 200 020 Selected Altitude feet 65536 16 1.0 100 200 029 DC Current (Battery) amps 256 8 1.0 100 200 0A1 Selected Altitude feet 65536 16 1.0 100 200

9 Chapter 1 ARINC 429 Tutorial

Each data item that can be transmitted is assigned a label selected altitude or DC current depending on the equipment code, and these are listed in ARINC Specification. Examples of ID. Table 7 and Table 8 also show the parameters which iden- labels are shown in Table 7 for BCD and Table 8 for BNR. tify the units of measure, the range or scale, the significant digits (BCD) or bits (BNR), the positive sense of the quantity, its Labels may be associated with more than one equipment resolution, maximum and minimum transit interval, and for type, and the equipment IDs associated with the examples some labels, the maximum transport delay. are shown in Table 9. Thus BCD label 010 is always present latitude, but it can pertain to three different sources, the Typically, messages are sent repetitively. For example, Flight Management Computer, the Inertial Reference System, measured airspeed is transmitted from the sensor to the or ADIRS. BCD label 014 is either Magnetic Heading from the instrument at intervals not less than 100 milliseconds or Inertial Reference System, Attitude and Heading Reference greater than 200 milliseconds. Messages may also be sent in System, or ADIRS. repetitive word sequences or frames. Messages from each In Table 8 BNR label 064 is the nose tire pressure from the fuel tank level sensor are sent in sequence, and then the Tire Pressure Monitoring System. BNR label 102 can be sequence is repeated after a specified time. The specific data Table 9. Equipment IDs for Tables 6 and 7 source to which the data applies is determined either by the Label or the SDI. Equipment ID (Hex) Equipment Type 002 Flight Management Computer Table 10 shows label 241, which is transmitted approximately 004 Inertial Reference System once per second. The sequence shown starts with the left 005 Attitude and Heading Reference System main tank followed by the right and then center. Once the 020 DFS System 63-word sequence is completed, it repeats, starting over with 029 ADDCS and EICAS word 1. Most of the data is in BNR format, but some words 038 ADIRS 03C Tire Pressure Monitoring System are in BCD. 0A1 FCC Controller Bit Oriented Protocols The Williamsburg, or “bit oriented”, Protocol is a system

Table 10. Message Sequence for Label 241

Word Signal Units Range Sig. Digits Resolution Data 1 Left Main Tank #1 pF 319.922 12 .078125 BNR 2-13 Left Main Tanks #1 to #13 pF 319.922 12 .078125 BNR 14 Left Main Tank #14 pF 319.922 12 .078125 BNR 15 Left Main Bite Cap. No. 1 pF 319.922 12 .078125 BNR 16 Left Main Compensator pF 319.922 12 .078125 BNR 17 Load Select 10,000 Lb. 0-90000 1 10,000 BCD 18 Load Select 1,000 Lb. 0-9000 1 1,000 BCD 19 Load Select 100 Lb. 0-900 1 100 BCD 20 No Data Transmitted 21 Left Main Fuel Density Lb./Gal 8,000 12 .000977 BNR 22-42 Repeat Words 1-21 for Right Tanks 43-53 Repeat Words 1-21 for Center Tanks 54-58 No Data Transmitted 59 Load Select 10,000 Lb. 0-90000 1 10,000 BCD 60 Load Select 1,000 Lb. 0-9000 1 1,000 BCD 61 Load Select 100 Lb. 0-900 1 100 BCD 62 No Data Transmitted 63 Center Tank Density Lb./Gal 8,000 12 .000977 BNR

10 for transferring files between ARINC units. It was originally use the bit-oriented system it transmits a message using the defined in ARINC Specification 429-12 and expanded in latest version of which it is capable. A handshaking process Specifications 429-13 and 14 and is further defined in Refer- adjusts the protocol to the lowest common denominator that ence 5. It is currently under revision. It should be used in lieu both sending and receiving systems can use. Currently, two of the former AIM, file transfer, and maintenance formats versions of the Protocol are available. Version 1 is defined in used in Specification 429-11. Normal ARINC data messages 429-12 and refined in 429-13. Version 2 is defined in 429-14 can be intermixed with the bit-oriented messages of the Wil- but was never used. Reference 5 deletes Version 2 and it liamsburg Protocol. defines a new Version 3. It redefines Version 1 to facilitate the communications of the ACARS Management Unit (MU) and A start up procedure is used to determine the proper proto- the Satellite Data Unit (SDU). col for transferring data. When a system element wants to The source initiates communications by sending certain pre- defined codes. If a bit-oriented transfer is desired, the initial

Airline Airline Source RTS Word Source

Original CTS Word Data File SOT Word 1 Data Word 2 First LDU “ ” n Data Word 254 EOT Word 256

ACK Word

RTS Word

CTS Word

SOT Word 1 Data Word 2 Data Word 3

Received EOT Word 4 Data File

ACK Word

Figure 8 File Transfer Scheme Version 1 (no Windows)

11 Chapter 1 ARINC 429 Tutorial code word will be an “ALO” (for Aloha) signal to the potential CTS, the source initiates a Version 1 transfer with a Start of recipient. The ALO word should be sent by any system that Transmission word (SOT). The SOT includes a file sequence supports the protocol just after the system powers up, or per- number, a General Format Identifier (GFI), and a LDU forms a re-initialization for any reason. If any sink is capable Sequence Number. The data words are then sent, followed of receiving bit-oriented data it responds with an “ALR” by the (up to) 255th word which is an End of Transmission code so that the source knows that it can transmit to that (EOT). Each LDU transfer (255 words or less) is terminated unit. When a source wants to transmit to a unit capable of by an End of Transmission Word (EOT). The EOT includes a handling the protocol, it sends a Request to Send word (RTS), CRC and identifies the position of the LDU in the overall file and waits to receive a Clear to Send (CTS). The RTS includes a transfer. The sink performs a verification process on the EOT Destination Code and a Word Count, which are repeated in and sends an Acknowledgment Word (ACK) if all tests are the CTS for verification. If the CTS is correct, the source then passed. The source then sends another CTS, and the process initiates the file transfer, following the sequence shown in is repeated until the last LDU is acknowledged. Figure 8 for version 1. The latter version provides the capabil- ity of sending a larger file (up to 7 LDUs), without needing to renew permission of the sink. ARINC 419 Reference 7, ARINC 419 Digital Data System Compendium, Files are transferred in blocks called Link Data Units (LDU) ranging in size from 3 to 255 words. Following receipt of the

Table 11. Systems Using Bit Oriented Communications and Their Address Labels

SYSTEM SAL (OCT) SYSTEM SAL (OCT) 777 CABIN INTERPHONE SYSTEM 152 LOW SPEED DATA LINK (ARINC 603) 300 747 DFDR AND A330/340 SSFDR 163 FMC 1 300 DFDAU (Mandatory Load Functions) 170 FMC 2 301 SDU #2 173 DFDAU (AIDS) 302 RFU 174 CFDIU 303 HGA/HPA TOP/PORT 175 ACARS MU/CMU (724B, 748) 304 HGA/HPA STARBOARD 176 WBS 305 LGA/HPA 177 TCAS 306 GPS/GNSS SENSOR 201 SDU #1 307 MCDU 1 220 CABIN TELECOMMUNICATIONS UNIT (CTU) 334 MCDU 2 221 HF DATA RADIO/DATA UNIT #1 340 MCDU 3 222 HF DATA RADIO/DATA UNIT #2 344 PRINTER 1 223 ACESS 360 PRINTER 2 224 EFIS 361 HIGH SPEED DL (ARINC 615) 226 ENGINE INDICATION UNIT 365 MCDU 4 230 CABIN TERMINAL 3 372 EIVMU 1 234 CABIN TERMINAL 4 373 EIVMU 2 235 CABIN TERMINAL 1 374 EIVMU 3 236 CABIN TERMINAL 2 375 EIVMU 4 237 OMEGA NAV. SYSTEMS 376 CABIN VIDEO SYSTEM (AIRSHOW) 266

12 Chapter 2 Other ARINC Protocols describes a number of digital transmission system build- during the development of ARINC Characteristics 561, “Air ing blocks which where available prior to 1984. It provides a Transport Inertial Navigation System”. ARINC 568 uses the synopsis of many protocols that predate ARINC 429 such as same electrical interface as ARINC 561. ARINC 561, 582, 573 and 575. A six-wire system involving 3 pairs of wires, was used in 561. The reference describes a number of digital transmission The three pairs served as “clock”, “sync”, and “data” respec- systems with varying standards. Some systems used 32-bit tively. Non return to zero (NRZ) was employed, and a 12 volt words similar to ARINC 429; some used major frames of four logic level was transmitted for a binary 1. The word length subframes each consisting of 64, 12-bit words. Still others was 32 bits. Bits 32 and 31 contained the SSM, and no parity used 32-bit, rather than 64-bit words. Some message frames bit was provided. The remaining fields included an 8-bit label were 24 bits with three subframes of two BCD words. Some and 6 BCD fields, five of 4 bits and one of 2 bits. In 1967 the systems did not provide information identifiers; others used 6-wire system was adopted as an industry standard. 8-bit label codes, and another depended on time slots for ARINC 573 identifying information. Identification of BCD vs. BNR was Other standards include ARINC 573, a Flight Data Recorder provided by a flag bit in either the 1st bit or the 4th bit transmitted. A variety of standard data labels were adopted.

Some electrical interconnections depended on one wire per bit; others used the 6 wire system described above while others used a shielded 2 wire twisted pair or a coaxial cable. Either two state, (HI LO), or three state (HI NULL LO) were used. Voltage levels ranged from 18.5 to 10 for the high state and from (less than) 5 to 1 for the null where used. Digital languages included Gilham code (an example is the altitude encoder for the ATC Transponder), a bit stream you determined in each individual case, International Standards Figure 9 ARINC 561 6-Wire Bit Encoding Organization (ISO) Alphabet #5, BCD, and BNR. In some cases there was no error detection or correction, others used bit output format. This device sends a continuous data stream parity or character parity, or block sequence check. Bit rate of Harvard Bi-Phase encoded 12 bit words which is encoded varied from 384 bps to 12+ Kbps, and there were many other in frames. The data in a frame consists of a snapshot of the variations among systems. many avionics subsystems on the aircraft. Each frame contains the same data at a different snapshot in time. The variability of “standards” doesn’t matter where a single user is involved, but is very important when equipment from Each frame is broken into four sub-frames. At the start of different suppliers must interact with each other. Standard- each sub-frame is a unique sync word that is used by the ization is beneficial not only to the aircraft integrator, but to receiver to synchronize with the incoming data. the equipment supplier who can have greater assurance of ARINC 575 product acceptability so long as it is “on spec”. ARINC 429 is the most widely applied Digital Data Transmission specifica- ARINC 575 is an older specification very similar to ARINC 429 tion for modern transport aircraft. ARINC 429 draws on the experience of 419 but does not depend on it.

1 bit cell ARINC 453 5v Not a formally released specification. See ARINC 708. ARINC 561/568 0v 11001010 The need for standardized digital data transmission arose

Figure 10 Harvard Bi-phase Bit Encoding

13 Chapter 2 Other ARINC Protocols but now obsolete. It accommodated the Mark 3 Subsonic Air is used on the new Boeing 777 Aircraft. It uses a high-speed Data System (DADS) with a single twisted pair of wires, which bi-directional bus capable of either periodic or aperiodic has become the standard in ARINC 429. Electrically, ARINC transmissions. Access to the bus is controlled by a sophisti- 575 is generally compatible with low speed ARINC 429. Some cated protocol involving wait periods, quiet periods and other variants of 575 use a bit rate that is significantly slower than rules. Further details can be found in Reference 9. ARINC 429 and are not electrically compatible. Also, in some cases, ARINC 575 words use bit 32 as parity (as does ARINC ARINC 708 429); in other cases bit 32 is used as data. This protocol is specific to airborne weather radar systems. It is used as the output from the radar to the radar display. ARINC 582 The bus uses 2-wires, is simplex, Manchester encoded and This is an older specification that has many electrical per- runs at a one-megabit data rate. It was originally based upon mutations. There are 6-wire versions (see ARINC 561), 2-wire a simple derivative of MIL-STD-1553 technology. The data versions (see ARINC 575) as well as 16-bit, 2-wire versions. words are 1600 bits long which is composed of one, 64-bit status word and 512, 3-bit data words. ARINC 615 Special cases of ARINC 429 compliant systems also exist. ARINC 717 ARINC 615 (See Reference 8) describes a high-speed data ARINC 717 supercedes ARINC 573 and is used to perform loader to transfer information to and from on board digital the same function. It adds a number of different bit rates systems. It is a software protocol layered on top of an ARINC and frame sizes. It also provides for an alternate output data 429 physical layer. There are two versions of the loader. PDL stream that is identical to the primary, Harvard Bi-phase is a portable flight line piece of test equipment and ADL is encoded stream, except that it is encoded in BPRZ format designed to fit in commercial aircraft instrument panels. Both (the same as ARINC 429). versions of equipment are capable of reading and writing to 3½ inch diskettes and transferring data between the diskettes and a selected airborne computer. The transfers can occur automatically, or via an ARINC 429 data bus. Data can be either uploaded or downloaded as desired.

ARINC 629 Additional ARINC standards are being developed. ARINC 629

14 Appendix A References

List of References

• ARINC Web Site, http://www.arinc.com • ARINC Specification 429P1-15, September 1, 1995 • ARINC Specification 429P2-15, March 6, 1996 • “Principles of Avionics Data Buses”, Editorial Staff of Avi- onics, Communications Inc., Leesburg, VA • AEEC Letter 97-013/WIL-03, January 24, 1996 • ARINC Digital Data System Compendium, ARINC Report 419-3, November 5, 1984 • ARINC Airborne Computer Data Loader, ARINC Report 615-2, June 1, 1991 • “ARINC 629 P1-4 Multi-Transmitter Data Bus”, “Part1, Technical Description”, December, 1995 • Aeronautical Radio, Inc., 2551 Riva Road, Annapolis, MD, 21401 • Global Engineering Documents

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